1. Field of the Invention
The present invention concerns a method for preventing metal material from oxidation in case of melting low fusion point nonferrous metal such as zinc, magnesium or their alloy in a melting vessel for injection molding.
2. Detailed Description of the Prior Art
As oxygen in the atmosphere deposits, sticks or adheres as oxidation surface layer to the surface of granular metal and oxygen in the atmosphere tends to be born with metal material during the supply, the metal material is susceptible to be oxidized, even melted in a melting vessel, when heated and melted in the melting vessel as it is.
When melt metal is oxidized, metallic splash caused through agitation adheres and lies on the vessel inner wall and agitation member or others, as impure oxidized sludge, causing malfunction of agitation member or plunger, or mixing into the melt metal as impurities with oxides of the melt metal surface, provoking deterioration of injection molded metal products.
Therefore, the oxidation is controlled by reducing the oxygen concentration in the melting vessel by sucking atmospheric oxygen with a vacuum pump during the material supply, or supplying in the melting vessel with inactive gas such as argon all the time to heat and melt metal material in the inactive gas atmosphere. However, as for oxygen due to surface oxidation of the metal material caused in the natural state, the metal material is heated and melted as it is, because it is extremely little, and there is no effective exclusion means.
In this situation, if the melting is performed during the material supply, the oxygen concentration in the melting vessel increases to accelerate the oxidation of the melt metal surface, even in the inactive gas atmosphere. Existence of oxygen due to the surface oxidation is believed to be one cause of the increase of oxygen concentration and even if its quantity is small, it will end by exceeding the prescribed value of oxygen concentration, so it is earnestly desired to lower below the prescribed value by any means.
The present invention has an object of providing a novel oxidation prevention method of melt metal in the melting vessel and an apparatus allowing to solve the oxidation problem during the melting of metal, by suspending both heating and supply of metal material under the monitoring by measuring the oxygen concentration in the inactive gas atmosphere.
The oxidation prevention method of the present invention for solving the problem is a method for melted metal material by a melting vessel, comprising inside a rotatable agitation member having a weighing chamber communicating with a nozzle member and an injection member advanceably and retractably inserting an extremity injection plunger passing through the agitation member in the weighing chamber, and the melting vessel being installed on a slant with the nozzle member downside, comprising the steps of; making a space area over the melted metal surface of the melting vessel into inactive gas atmosphere, measuring and monitoring the oxygen concentration in the space area, judging as error when the measured oxygen concentration exceeds a predetermined reference value, and stopping heating and material supply.
The oxidation prevention apparatus of the invention is the one having a weighing chamber communicating with a nozzle member, comprising inside a rotatable agitation member, and an injection member advanceably and retractably inserting an extremity injection plunger passing through the agitation member in the weighing chamber, wherein a supply tube at a supply inlet of a melting vessel installed on a slant with the nozzle member downside is erected, a supply apparatus of granular metal material is connected to the supply tube and, at the same time, a gas piping for supplying to a space area over the melted metal surface of the melting vessel with inactive gas atmosphere is disposed in the supply tube or at a top portion, and an oxygen detector having transmission function is mounted on the supply apparatus over the supply tube by facing an oxygen sensor in the supply tube.